This manga is pretty cute. The drawings are nice, and the jokes are pretty good. The humor style reminded me a lot of Azumanga Daioh (I can't explain why, it just does), so if you liked the humor from that one, you will probably think this one is pretty funny too. The one thing that's weirdest about it, though, is that it's awkward that it's about music, since in a manga you obviously can't hear it, you know?
There are two specific criticisms I have: 1. Mugi's little yuri fantasy obsession should be eliminated completely; that kind of thing is just plain cheesy. 2. About the advisor, Sawako... I know that the perverted lech teacher is a common source of comic relief in a school manga, but... she's just too much of a jerk about the way she does it, that I end up being irritated and angry at her instead of amused.
Despite the couple of flaws, I thought this manga was overall cute and enjoyable. If you are looking for some light, entertaining school life series, I recommend giving this a try. Ah, I guess I should mention though, the music aspect in this series is more like a theme than the primary focus--that is, if you're looking for something that is really intensely about music, this is probably not what you want.